Explosive weapon casing and method of making same



July 13, 1965 J. T. PAUL, JR 3,194,158

EXPLOSIVE WEAPON CASING AND METHOD OF MAKING SAME Filed March 26, 1958 3 Sheets-Sheet 1 co r G N m 0 N cu r m D n 1,

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INVENTOR. JAMES T. PAULJR.

BY 77% M,

ATTYS Jul); 3113, 1965 J. T. PAUL, JR 3,194,158

EXPLOSIVE WEAPON CASING AND METHOD OF MAKING SAME Filed March 26, 1958 3 Sheets-Sheet 2 IO 5. Q

m N N N E! CO H m w N ml (D I l ("3 cm on U n m I-I Q2| U L Z3 5 5 a, N LL. I (0| n L D N co 2 93 INVENTOR.

JAkMZEi T. PAULJR. BY

WkQBQU -W July 13, 1965 J. T. PAUL, JR 3,194,158

EXPLOSIVE WEAPON CASING AND METHOD OF MAKING SAME Filed March 26. 1958 5 Sheets-Sheet 5 FIG.4.

FIG.6.

INVENTOR. JAMES T. PAUL JR.

ATTYS and in which:

United States Patent This application relates to ordnance manufacture and more particularly to a weapon casing which is itself explosive and a method of making the casing.

A conventional steel weapon casing contributes significantly to the overall weight of the weapon but does not add to the total explosive force of the weapon. Furthermore, steel is a strategic material which is likely to be in short supply in times of conflict.

Steel casings in mines are subject to the additional disadvantages that the c-asings may be slowly corroded and eventually allow the sea Water to leak into the casing and destroy the mine actuating mechanism. Furthermore, a steel casing requires that special precautions be taken to avoid magnetic shielding of the detecting and actuating system if the system is responsive to the magnetic field of a ship. Additionally, a steel mine casing is more susceptible than a plastic casing to detection and destruction by countermeasure devices.

Accordingly, it is an object of this invention to provide an ordnance casing which is explosive in character and augments the explosive force .of the main charge of the ordnance device.

Another object is the provision of a light weight weapon casing which is constructed of readily available structural materials and a method of fabricating said casing.

Yet another object is the provision of a new and ime provedweapon casing which is impervious to salt water corrosion and is composed of non magnetic materials.

A further object of the instant invention is to provide a novel process for fabricating a reinforced resin casing of optimum strength. i

A still further object is the provision of anovel process for making and forming a .casinghaving a substantial quantity of explosive incorporated therein.

These and many other objects will become more clearly apparent when the following specification is read in conjunction with the attendantdrawings wherein like numerals designate like parts throughout the several views FIG. l is a perspective view of the equipment suitable for making Weaponcasings according to the teachings of this invention; I

FIG. 2 is a longitudinal section of the mandrel for forming the core which shows a core wound on said mandrel; f

FIG. 3 is a longitudinal section of a casing immedi ately prior to removal of the mandrel shaft; FIG. 4 is a plan view of the wiping edge of the doctor blade viewed from below; r

FIG. 5 is a section through the doctor blade; and

FIG. 6 is -a sectional viewv of the mold forforming the reinforcing rings showinga ring in the mold cavity.

In order to more clearly illustrate the principles of this invention, it will be described in detail with reference to but one embodiment thereof. It will be apparent to those skilled in'the art,.however, that it is not so limited but is susceptible of many alterations and modifications and .may be employed advantageously in the design and manufacture of a variety of o'rdnancedevices.

A weapon casing of the type herein disclosed should contribute to the explosive force of the weapon. It must not weather and in some instances it is required to withice stand prolonged exposure to salt water without deteriorating. Furthermore, it should be light in weight and possess rather low sensitivity to shock in order to decrease the probability'of detonation during handling. It must be mechanically strong and in some instances it may be essential that it be easily machined.

In order to obtain the optimum explosive characteristics, an explosive such as .RDX is incorporated into a shaped casing of plastic or resin.

A series of tests wer conducted to evaluate the suitability of various RDX filled resins for use as a weapon casing. Ethyl acrylate proved to be unsuitable because it did not cure rapidly at allowable temperatures. Other acrylic resins were more suitable in that respect. For example, butyl methacrylate and ethyl methacrylate were tested at 1700 p.s.i. and 1800 p.s.i. tensile strength respectively at contents of 50% RDX and found to be more suitable for the purpose than ethyl acrylate.

Certain polyesters containing bifunctional acids and alcohols are characterized by molecular structures terminating in hydroxyl groups which may be reacted with diisocyanates to thereby link several molecules to form a high molecular Weight polyester polyurethane. In the presence of water, urea type links will also be formed and through these links cross linking may be established by reaction of isocyanate with the amine hydrogen of the ureide nitrogen atoms. The chemical properties of these polymers make possible the creation of a wide range of molecular structures with some degree of control. Products ranging from elastomers to hard, tough, rigid plastics have been successfully made; for example, a sebacic acid-ethylene glycol polyester reacts with m-tolylene diisocyanateto yield a hard, tough plastic.

The best resin for fabricating an RDX containing, casing was found to be the so called Stypol series of resins which are styrene modified type of these polyesters. Accordingly, Stypol 705 was selected as one preferred resin for practicing this invention. Several accelerators were evaluated for use in combination with Stypol 705. The catalysts tested were each mixed with a 42% Stypol 705- 58% RDX slurry and cured overnight at 50 C. Surface conditions of all samples were examined. All catalyst systems tried except those containing DDM (methyl ethyl ketone peroxide) and cobalt Nuodex (napthenate, 6% cobalt) exhibited soft or tacky surfaces.

Fiberglass reinforced cylinders made using several of the catalyst systems corroborated the results obtained using the unreinforced slurry.

The pot life of a slurry of Stypol 705 and DDM and /2% Nuodex at 35 C. is 1 hour which allows a reasonable working period for-the resin even at relatively high temperatures.

Since the polymerization of Stypol series of resins is exothermic, their use may create a hazard during curing of the resin. The system reaches a maximum temperature shortly after the gelatin of the resin ocurs; this maximum is limited by the heat capacity of the RDX incorporated within the system. Thus for a given concentration of RDX and-resin, a certain predetermined temperature rise may be expected. Should this temperature become too great, there is a danger that the RDX will decompose exothermally detonating the entire system. Adiabatic' polymerizations of RDX-Stypol 705 mixtures were carried out to determine the maximum temperature attained during polymerization. Fortunately, at a starting temperature of 55 C., systems containing 60% RDX gave maximums of only 107 .C. which are well below the temperature required to detonate the system.

Three types of weapon casings were considered and evaluated; the first type was a cast resin-RDX structure. This type lacked the necessary strength, while the second type, laminated nitrated cloth or yarn bonded together by a suitable resin, possessed only marginal strength. A glass yarn reinforced, explosive containing resin was selected as the most appropriate type for a weapon casing.

Glass yarn reinforced casings containing aluminum in the form of filaments or powder were evaluated with the expectation that the incorporation of aluminum would increase the peak detonation pressure of the weapon without a sacrifice in strength. No effect on strength was noted, however the incorporation of aluminum in a Stypol 705 resin mixture containing substantial quantities of RDX makes the mixture more sensitive than pure RDX. For that reason, it is not desirable to incorporate large amounts of aluminum into a mixture containing large quantities of RDX.

It is advantageous at this point to refer to the drawings in order to more readily understand this invention. The apparatus for forming the weapon casing comprises a shaped, ported mandrel 11. Optionally, the mandrel may be secured at either end to nose piece 12 and tail piece 13, in the event it is desired to utilize partly preformed tail and end pieces.

The nose piece 12 is composed of Phenolite (a canvas reinforced phenol formaldehyde resin) which is reinforced by an aluminum ring 14 for added rigidity. The nose assembly is faired into the mandrel along the peripheral line A-A to form a smooth continuation of the mandrel upon which to wind the glass reinforcing yarn. A relief portion is formed in the nose piece 12 to provide a cusp 16 which facilitates deposition of the glass filaments. The nose piece 12 and the insert 14 in turn support a necked and threaded end 18 of mandrel shaft 19 while a similar threaded end 21 is formed at the opposite end of shaft 19.

The tail piece 13 is also composed of Phenolite and fits against the rear peripheral edge of the mandrel 11 along line BB to provide a smooth continuation of the mandrel. A shoulder 22 extends some distance beyond the diameter of the mandrel to provide a rear stop for the filament winding. The reinforcing filaments are ultimately wound to a thickness equal to the height of shoulder 22. The piece 13 is also threaded interiorly to receive a cover plate 23 having an aperture therein to receive the end 21 of shaft 19.

A pair of wooden supporting spiders 24 and 26 positioned within mandrel 11 provide additional support for the shaft 19.

The ends 18 and 21 are connected to shafts 27 and 28 respectively in any suitable manner. The shaft 27 is rotatably connected to and driven by a suitable source of power 29 while shaft 28 is rotatably supported in a journal bearing 31 which is slidably carried on the bed 32 by the platform 33. A locking member 34 prevents sliding of the journal bearing during the formation of the casing as mandrel 11 is rotated.

A core composed of resin reinforced by glass yarn is formed by building up layers of glass yarn and simultaneously applying a resin mixture with the doctor blade 36. This doctor blade 36 is composed of a blade portion 37 having a wiping edge 53 formed from a thin flexible piece of metal and soldered and bolted to a back up plate 38 which is formed in three separate sections to allow the blade portion to flex during the lay down of the casing.

Since it is desirable to attach the core of the casing to the Phenolite nose and tail pieces 12 and 13 by winding the glass yarn about these pieces, the Phenolite must be coated with a substance to prevent it from inhibiting the polymerization of the polyester. A layer of m-tolylene diisocyanate is brushed on the Phenolite just prior to the beginning of the winding operation to prevent this undesirable effect and to increase the strength of the bond between the Phenolite and the Stypol resin.

In winding a weapon casing, an inert core is first made on mandrel 11, which core later serves as the mandrel upon which the remainder of the casing is laid down. Accordingly, the mandrel 11 is prepared by coating it with a silicone grease and then helically laying down a strip of cellophane until the entire mandrel is covered. Prior to this, the Phenolite nose and tail pieces 12 and 13 are degreased with trichloroethylene, for example, and coated with m-tolylene diisocyanate for the purposes set forth hereinabove.

One complete layer of glass yarn filaments 39 is wound onto mandrel 11 of spools 41 while a plurality of tensioning pulleys 42 control the tensions on the yarn strands as they pass to yarn guides or combs 43. Only a few of the guides 43, pulleys 42 and spools 41 are shown in order to simplify the drawing and make it more readily understood. The combs 43 are mounted on a platform 44 which reciprocates along the guideway 46 of bed 32 in predetermined time relation with respect to the rotation of the mandrel 11. The reciprocating platform is driven by the power source through a chain and sprocket arangement 47 and 48. The ratio of the speed of reciprocation of the platform and the speed of rotation of the mandrel 11 determines the angle at which the glass yarn is laid down upon the mandrel. When the speed of rotation is high compared with the rate of reciprocation of the platform the pattern of the yarn on the mandrel is nearly that of a right circular cylinder, as the ratio of speed of rotation to rate of reciprocation is decreased and the angle between the yarn on the mandrel and a radial plane of the mandrel increases.

Each yarn guide receives several filaments and spaces them at a predetermined distance apart-usually about 1.5 mm. Therefore a plurality of swaths of yarn are deposited on the mandrel corresponding to the numbe of guides 43 on the traveling platform 44. Yarn guides may be added all around the circumference except where the doctor blade 36 is located.

The yarn should be applied to the mandrel 11 at about 30 to a plane normal to axis of the mandrel. At smaller angles the casing will fail in service due to bending moments encountered in use especially if the casing is employed in a depth charge. Although making this angle greater will increase the strength of the casing, when the angle is increased much beyond 30 it has a tendency to slip on the mandrel as it is wound thereby increasing the difficulty of fabrication.

After one complete layer of glass yarn is laid down, the mandrel is stopped and the doctor blade 36 is moved into position adjacent to the mandrel. The space between the mandrel and the blade is filled with resin either by hand or from a suitable reservoir. The doctor blade scarcely touches the yarn at the mid point of the mandrel so that there is a small space near the ends of the mandrel since the diameter of the mandrel is slightly greater at the center to permit more facile removal of the core therefrom. The backing of the doctor blade 36 is constructed of three sections 48, 49 and 51, the nose, body, and the tail section respectively. A slight space left between the backing plates supporting the blade portion 37 allows the wiping edge 53 to flex during the lay down of the core. When the doctor blade is first moved against the mandrel, the ends 48 and 51 tend to move in further than the center section 49 but as the winding continues the shape of the blade conforms to the shape of the weapon casing thereby providing a heavier casing cross section progressing from the center section toward the ends. The wiping edge 53 of the blade is tapered on its under surface to prevent dripping of the resin and the end portions 49 and 52 are fitted with thin plates 54 formed to the contour of the nose and tail to prevent the resin from spilling over the edge of the blade.

The rotation of the mandrel is then resumed for a predetermined number of yarn circuits on the mandrel. About 420 revolutions of the mandrel as indicated by counter 56 are needed to produce a core 0.050 inch thick. The mandrel is then stopped momentarily, drive to platform 44 is disengaged, and the manrel is rotated slowly by hand until the yarns follow a cylindrical path at those spots at which there appears to be insufficient yarn. The yarn is then cut and the mandrel is rotated at high speed to pull theloose ends into place, after which the blade is eased away from the core. In the later stages of the winding it is desirable that the resin be judiciously added to the doctor blade in small quantities'so thatthere will be none left when the winding is complete and the doctor bladeis moved awayfrom the core. i i i The core is cured in situ' by slowly rotating the mandrel and applying heat from source 57 which may conveniently be a battery of infra-red lamps. After the core is completely cured, the end plate 23 is removed and an air line is attached to the tubing 58 disposed within mandrel 11 through the spider 26, the air vents through port 59 in the mandrel and tends to loosen the core from the mandrel- A cutting tool (not shown) is then moved into position against the 'core to cut it into two sections as the mandrel is slowly rotated. Thecore. is removed" from the mandrel in two sections; the interior of the core is then sand ed to remove any cellophane which became stuck to the core during thewinding operation. A plurality of reinforcing rings 62 are inserted within the core and glued in place by a suitable adhesive. The core itself is reglued along the cut line. It is desirable to glue one reinforcing ring along the out line 63) to strength that joint.

The rings 62 are also formed of a similar glass reinforced polyester resin. The rings are cast in a mold 64 which is formed in two complementary halves 66 and 67 to permit more rapid ejection of the finished ring. The finished rings have a flat exterior circumference and are hemispherical in cross section at the interior circumference to permit more efficient filling of a casing when the rings are in position within a finished casing since voids and air spaces in the explosive filling at the line ofv joinder of therings and the interior of the casing areeliminated- After thecore is reassembled in the aforedescribed manner, it is'again mounted on the appropriate shafts 27 and 28 and is coatedwith a layer of yarn. The doctor blade is moved into positionand a clutch 68 between the power source 29 and the blade back off drive 69 is engaged so that the back off cams 7'3 rotate at a predetermined speed to gradually withdraw the blade from the core as thewinding proceeds.

The strength of the laminated casing is inversely proportional'tothe diameter of the" glass yarn strands forming it. Furthermore, a larger quantity of RDX can be incorporated into the structure at a given strength when the glass yarn diameter is small. Accordingly, it is usually desirable to employ reinforcing yarns .of very small diameter in forming the casing.

A slurry comprising RDX, Stypol and a small amount of catalyst is introduced onto the doctor blade 36 to form a bead of explosive-resin mixture and the winding operation is commenced. Sufficient slurry is continuously added to the blade to maintain a constant supply of slurry on the blade during the run, except at the termination of the winding operation when it is desired that the resin be all used up. By forming the casing in the manner described, the strength of the finished product is unusually high. A principal reason, is that by first forming the core and then using the core as a mandrel, it is not necessary to cut the entire piece to remove it from the mandrel and then reglue it. Only the thin core is cut, accordingly the piece is not weakened along the glue line. The maximum amount of RDX which can be incorporated in a laminating slurry of resin and RDX depends upon the particles size of the RDX; at a particle size of 40 microns the maximum amount of RDX is 67% by'weight; at a particle size of 150 microns the percent of RDX obtainable in the slurry is 71%. Within limits, a change in the winding pattern or in the tension on the yarn has less effect on the amount of glass present in a given structure than previously thought. However, by varying the pressure of the doctor blade against the casing being wound it is possible to vary the percentage of the glass yarn from 10% to about 50%.

For example, two casings were made, one at a blade pressure of250 gm./in. of blade length and another at 500 gm./in. of blade length the former contained 20% yarn while the latter contained 35% glass yarn.

After a casing of about 0.500 inch in thickness is built up on the core, the flow of resin onto the core is stopped and a layer of yarn is wound on the wet casing. This outer layer is coated with a resin not containing RDX to give a glossy surface with a slight helical yarn pattern in it. The casing 72 is then heat cured, removed from the shafts and is ready to be capped and filled with explosives or the like.

In the event however that it is necessary to machine the casing, it can be turned down on a lathe by following conventional shop practice except that it is necessary to use large amounts of kerosene coolant during the machining. This desensitizes the explosive chips which tend to'become sensitive to shock as they are formed.

It is not to be inferred from this that a casing containing large amounts of RDX is overly sensitive to shock and heat. In the physical form of a large piece such as a casing it is' only about as sensitive to shock as cast TNT and may be subject to normal handling without the danger of premature detonation.

Although this invention has been described with reference to a single preferred embodiment thereof it is not limited as it is susceptible of many modifications and variations without'departing from the spirit and scope thereof. Therefore the scope of this invention is to be determined only by the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is;

1. The process of fabricating an explosive structure which comprises; winding a plurality of glass filaments on a mandrel, applying a potentially thermosetting resin slurry to the glass filaments on the mandrel, curing the resin to form a glass-reinforced resin core, removing the core from the mandrel, winding a plurality of additional glass filaments on the core and concurrently therewith applying to the last-named wound filaments a slurry comprising a high explosive and a potentially thermosetting resin, and curing the resin and explosive slurry onthe core to form a rigid explosive substantially hollow structure substantially integral with said core.

2. The process of fabricating an explosive structure which comprises; rotating a mandrel, winding one layer of glass filaments on said mandrel, applying a potentially thermosetting resin slurry on said layer of glass filaments and concurrently therewith winding glass filaments on said first layer to form a core of predetermined thickness, heating the core to cure the resin, cutting the core into two portions to facilitate its removal from the mandrel, removing the core from said mandrel, aflixing a plurality of core reinforcing members to the interior surface of said core, reuniting the two portions of said core, winding a plurality of glass filaments on the reunited core and concurrently therewith applying to the last named wound filament a slurry comprising a high explosive and a po tentially thermosetting resin, and curing the slurry on the core to form a substantially hollow explosive structure.

3. The process of making an explosive weapon casing which comprises; releasably securing a nose piece and a tail piece to a casing shaping mandrel, rotating said mandrel, winding a plurality of glass filaments in a helical pattern on said mandrel and said nose and tail pieces, applying a resin slurry to the glass filaments while the filaments are being wound on the mandrel, curing the resin to form a rigid hollow glass reinforced resin core secured to the nose piece and the tail piece, cutting the core into two portions on a line intermediate its ends to facilitate removal of the core from the mandrel, releasing the mandrel from said nose and tail pieces, removing the core from the mandrel in two pieces connected respectively to the nose and tail pieces, affixing a plurality of reinforcing rings to the interior surface of said core, placing a quantity of adhesive at the line on which the core was cut, winding a plurality of glass filaments on the core and concurrently therewith applying to the last named glass filaments a slurry comprising a high explosive and a resin, curing the resin in the slurry on the core to form a rigid explosive substantially hollow weapon casing.

4. The process of fabricating an explosive structure which comprises; releasably securing a phenol-formaldehyde nose piece and tail piece to a mandrel, coating the end and tail pieces with diisocyanate, concurrently applying a polyester resin and a plurality of glass yarns to said mandrel to form a glass yarn reinforced resin core, curing said core, removing said core from said mandrel, winding one layer of glass yarn on said core, winding a plurality of layers of glass yarn and concurrently applying to said last named layers of glass yarn a slurry comprising an explosive and a polyester resin to build up a structure of predetermined thickness, applying heat to cure the structure.

5. The process of fabricating an explosive structure which comprises; windinga series of glass filaments about a mandrel at 30 to the longitudinal axis of the mandrel, concurrently applying a polyester resin to the glass filaments on the mandrel, curing the resin to form a core, removing the core from the mandrel, winding a plurality of glass filaments on said core at 30 to the longitudinal axis thereof, concurrently applying a slurry composed of an explosive and a potentially thermosetting polyester resin, curing the slurry at a temperature insufficient to initiate the explosive, to thereby form a substantially hollow explosive structure.

6. The process of fabricating an explosive weapon casing comprising; forming a glass reinforced inert core, winding a plurality of glass yarns on said inert core, concurrently applying to said glass yarns a slurry composed of an explosive and a polyester resin to completely cover the core and form an uncured substantially hollow casing, applying a layer of polyester resin containing no explosive to the casing, curing the casing at a temperature insufficient to initiate the explosive.

7. A non-magnetic substantially hollow weapon casing comprising; a thin hollow inner core composed of a cured glass reinforced resin, a plurality of reinforcing members composed of a glass filament reinforced resin and disposed in contact with the interior surface of said core and secured thereto, and a relatively thick outer portion composed of glass filaments and a mixture of high explosive and a resin wound about and bonded to said core.

8. A non-magnetic structure comprising; a thin core portion composed of a resin and glass reinforcing filaments, a plurality of reinforcing rings afiixed to the interior surface of said core portion, said rings having a convex inner peripheral edge and a flat outer peripheral edge secured to the interior of said core portion, a relatively thick portion disposed about said core portion and secured thereto, said thick portion comprising a mixture of a resin and an explosive and a plurality of reinforcing filaments.

9. The structure of claim 8 wherein the mixture of resin, explosive and reinforcing filaments contains up to 71% explosive.

10. A non-magnetic substantially hollow weapon casing comprising; a generally cylindrical core composed of a polyester resin and a plurality of helically disposed core reinforcing glass strands, a plurality of reinforcing rings affixed to the interior surface of said core and secured thereto, a cylindrical casing wound about said core and secured thereto, said casing comprising a mixture of a polyester resin and an explosive, and a plurality of layers of helically disposed reinforcing filaments.

11. The weapon casing of claim 8 wherein the reinforcing filaments are disposed at a 30 angle to the longitudinal axis of the casing.

References Cited by the Examiner UNITED STATES PATENTS 695,809 3/02 Hawk 102-38 807,494 12/05 Du Pont 102-98 2,614,058 10/52 Francis 102-56 2,748,830 6/56 Nash et al. 154-83 OTHER REFERENCES Miller et al.: Fiberglas-Reinforced Plastic as a Rocket Structural Material, Jet Propulsion, vol. 26, No. 11, November 1956, pp. 969972.

BENJAMIN A. BORCHELT, Primary Examiner.

ARTHUR M. HORTON, SAMUEL BOYD, Examiners. 

7. A NON-MAGNETIC SUBSTANTIALLY HOLLOW WEAPON CASING COMPRISING; A THIN HOLLOW INNER CORE COMPOSED OF A CURED GLASS REINFORCED RESIN, A PLURALITY OF REINFORCING MEMBERS COMPOSED OF A GLASS FILAMENT REINFORCED RESIN AND DISPOSED IN CONTACT WITH THE INTERIOR SURFACE OF SAID CORE AND SECURED THERETO, AND A RELATIVELY THICK OUTER PORTION COMPOSED OF GLASS FILAMENTS AND A MIXTURE OF HIGH EXPLOSIVE AND A RESIN WOUND ABOUT AND BONDED TO SAID CORE. 